a bit more front-end performance improvement

- lots of time was in delete-duplicates and free-vars
  switched from lists to hash table
- increase size of flisp heap. 2MB is still small; this is free performance.
- more efficient loading of flisp system image. improves startup time by a
  tiny but measurable amount; about .05sec. every bit helps.
Merge branch 'master' of github.com:JuliaLang/julia